repair questions for tile floor in dining room (1890-1910?)

The dining room floor in our house is 1/4"X 2" X 4+" terra cotta tile laid very tightly edge to edge in a herringbone pattern wiht a border. I'm guessing this was from expansions before or after 1900 .

At first I thought it was over some kind of very thin old-fashioned clay and hair carpet padding (maybe damp at the time of installing? ) which had disolved into fibers and dust. But others have suggested the fuzz is just from decayed carpeting dog hair and dust and the tiles are just laid on concrete or "mud" only (the joists below are sistered to support it)

We saw the imprint of the underside of one of the broken tiles embossed on the fuzzy stuff - some one said "see, that's the cement" I said , "no, look, it rubs away; it's hairs and something." (mat? dog? carpet? very fine thinset? 100 years of dust?) I rubbed a small area only and the stuff moved and under it seemed to be a hard surface that looked whitish - cement? bleached-out wood?

Now that I think of it, the thinset under our current house kitchen's new tiles crumbled to sand when I took some tiles up - I thought it would be impossible to get them up but it was easy (they weren't grouted in yet) and I just assumed the layer had made up a bad batch. Is thinset supposed to crumble?

I could have it analyzed but what we really need to know is what should WE do? Leave it as is? - only a few in a quite large room are cracked or broken but the ingetrity of the fit is disturbed resulting in an agreeable clickity-clacking when one walks around the table. Husband wants to take it up and relay it wiht grout which would be a huge, huge job wiht a very different look. I would pry up the traffic pattern which is where the few cracked ones and broken ones are vaccuum in small sections and push in replacements as needed. We found some in a closet.

Comments? Should it be on thinset or is it OK as is and just repair small areas wiht - nothing? thinset? ??? I don't know if there is a subfloor or what it might be. From below, I see milled planks, maybe 3" or less. (Some of the house is much older, and there are logs wiht bark still on as joists)

The more I think about it the more I realize I don't know. We don't get the house until Feb.so I can't explore more just now and even then, don't have the experience or vocabulary to unravel the puzzle. Maybe someone out there knows about it already. Or maybe the answer is one of the above.

I have never ran into anything like you are discribing, I don't know what to tell you. Myy guess is to find out how it was ariginally installed and try to duplicate that method and material. Best of luck. Lair

Thanks, both of you, I've had a chance to look more carefully since we got access to the house. There are tiles laid on cement that is on floorboards (the joists are sistered below) There is so much hair - from carpet or dogs - that I thought it was weird old padding. Now I see that was maybe "too much thinking" on my part and also that there is obvious cement elsewhere under loose tiles. Anyway, it is not the first priority. When we take action, Lair, I will report here. Thanks again, Carol